Standard Endpoints

Artigo
06/11/2011

Endpoints are defined by specifying an address, a binding, and a contract. Other parameters that may be set on an endpoint include behavior configuration, headers, and listen URIs. For certain types of endpoints these values do not change. For example, metadata exchange endpoints always use the IMetadataExchange contract. Other endpoints, such as WebHttpEndpoint always require a specified endpoint behavior. The usability of an endpoint can be improved by having endpoints with default values for commonly used endpoint properties. Standard endpoints enable a developer to define an endpoint that has default values or where one or more endpoint’s properties does not change. These endpoints allow you to use such an endpoint without having to specify information of a static nature. Standard endpoints can be used for infrastructure and application endpoints.

Infrastructure Endpoints

A service may expose endpoints with some of the properties not explicitly implemented by the service author. For example, the metadata exchange endpoint exposes the IMetadataExchange contract but as a service author you do not implement that interface, it is implemented by WCF. Such infrastructure endpoints have default values for one or more endpoint properties, some of which may be unalterable. The Contract property of the metadata exchange endpoint must be IMetadataExchange, while other properties like binding can be supplied by the developer. Infrastructure endpoints are identified by setting the IsSystemEndpoint property to true.

Application Endpoints

Application developers can define their own standard endpoints which specify default values for the address, binding, or contract. You define a standard endpoint by deriving a class from ServiceEndpoint and setting the appropriate endpoint properties. You can provide default values for properties that can be changed. Some other properties will have static values that cannot change. The following example shows how to implement a standard endpoint.

public class CustomEndpoint : ServiceEndpoint
    {
        public CustomEndpoint()
            : this(string.Empty)
        {
        }

        public CustomEndpoint(string address)
            : this(address, ContractDescription.GetContract(typeof(ICalculator)))
        {
        }

        // Create the custom endpoint with a fixed binding
        public CustomEndpoint(string address, ContractDescription contract)
            : base(contract)
        {
            this.Binding = new BasicHttpBinding();
            this.IsSystemEndpoint = false;
        }

        // Definition of the additional property of this endpoint
        public bool Property
        {
            get;
            set;
        }
    }

To use a user-defined custom endpoint in a configuration file you must derive a class from StandardEndpointElement, derive a class from StandardEndpointCollectionElement, and register the new standard endpoint in the extensions section in app.config or machine.config. The StandardEndpointElement provides configuration support for the standard endpoint, as shown in the following example.

public class CustomEndpointElement : StandardEndpointElement
    {
        // Definition of the additional property for the standard endpoint element
        public bool Property
        {
            get { return (bool)base["property"]; }
            set { base["property"] = value; }
        }

        // The additional property needs to be added to the properties of the standard endpoint element
        protected override ConfigurationPropertyCollection Properties
        {
            get
            {
                ConfigurationPropertyCollection properties = base.Properties;
                properties.Add(new ConfigurationProperty("property", typeof(bool), false, ConfigurationPropertyOptions.None));
                return properties;
            }
        }

        // Return the type of this standard endpoint
        protected override Type EndpointType
        {
            get { return typeof(CustomEndpoint); }
        }

        // Create the custom service endpoint
        protected override ServiceEndpoint CreateServiceEndpoint(ContractDescription contract)
        {
            return new CustomEndpoint();
        }

        // Read the value given to the property in config and save it
        protected override void OnApplyConfiguration(ServiceEndpoint endpoint, ServiceEndpointElement serviceEndpointElement)
        {
            CustomEndpoint customEndpoint = (CustomEndpoint)endpoint;
            customEndpoint.Property = this.Property;
        }

        // Read the value given to the property in config and save it
        protected override void OnApplyConfiguration(ServiceEndpoint endpoint, ChannelEndpointElement channelEndpointElement)
        {
            CustomEndpoint customEndpoint = (CustomEndpoint)endpoint;
            customEndpoint.Property = this.Property;
        }

        // No validation in this sample
        protected override void OnInitializeAndValidate(ServiceEndpointElement serviceEndpointElement)
        {
        }

        // No validation in this sample
        protected override void OnInitializeAndValidate(ChannelEndpointElement channelEndpointElement)
        {
        }
    }

The StandardEndpointCollectionElement provides the backing type for the collection that appears under the <standardEndpoints> section in the configuration for the standard endpoint. The following example shows how to implement this class.

public class CustomEndpointCollectionElement : StandardEndpointCollectionElement<CustomEndpoint, CustomEndpointElement>
    {
         // ...

    }

The following example shows how to register a standard endpoint in the extensions section.

<extensions>
      <standardEndpointExtensions>
        <add
          name="customStandardEndpoint"
          type="CustomEndpointCollectionElement, Example.dll,
                Version=1.0.0.0, Culture=neutral, PublicKeyToken=ffffffffffffffff"/>

Configuring a Standard Endpoint

Standard endpoints can be added in code or in configuration. To add a standard endpoint in code simply instantiate the appropriate standard endpoint type and add it to the service host as shown in the following example:

serviceHost.AddServiceEndpoint(new CustomEndpoint());

To add a standard endpoint in configuration, add an <endpoint> element to the <service> element and any needed configuration settings in the <standardEndpoints> element. The following example shows how to add a UdpDiscoveryEndpoint, one of the standard endpoints that ships with .NET Framework 4.

<services>
  <service>
    <endpoint isSystemEndpoint=”true” kind=”udpDiscoveryEndpoint” />
  </service>
</services>
<standardEndpoints>  
  <udpDiscoveryEndpoint>
     <standardEndpoint multicastAddress="soap.udp://239.255.255.250:3702" /> 
  </udpDiscoveryEndpoint>
</ standardEndpoints >

The type of standard endpoint is specified using the kind attribute in the <endpoint> element. The endpoint is configured within the <standardEndpoints> element. In the example above, a UdpDiscoveryEndpoint endpoint is added and configured. The <udpDiscoveryEndpoint> element contains a <standardEndpoint> that sets the MulticastAddress property of the UdpDiscoveryEndpoint.